Local seed systems remain the fundamental source of seeds for many crops in developing countries. Climate resilience for small holder farmers continues to depend largely on locally available seeds of traditional crop varieties. High rainfall events can have as significant an impact on crop production as increased temperatures and drought. This article analyzes the dynamics of maize diversity over 3 years in a farming community of Yucatán state, Mexico, where elevated levels of precipitation forced farmers in 2012 to reduce maize (...) diversity in their plots. We study how farmers maintained their agroecosystem resilience through seed networks, examining the drivers influencing maize diversity and seed provisioning in the year preceding and following the 2012 climatic disturbance. We found that, under these challenging circumstances, farmers focused their efforts on their most reliable landraces, disregarding hybrids. We show that farmers were able to recover and restore the diversity usually cultivated in the community in the year following the critical climate event. The maize dynamic assessed in this study demonstrates the importance of community level conservation of crop diversity. Understanding farmer management strategies of agrobiodiversity, especially during a challenging climatic period, is necessary to promote a more tailored response to climate change in traditional farming systems. (shrink)

Here we study two connexive logics based on one of the conditionals introduced by Church in [4] and on some negations defined through falsity constants in the sense of Ackermann in [1].

To analyze which ethically relevant biases have been identified by academic literature in artificial intelligence algorithms developed either for patient risk prediction and triage, or for contact tracing to deal with the COVID-19 pandemic. Additionally, to specifically investigate whether the role of social determinants of health have been considered in these AI developments or not. We conducted a scoping review of the literature, which covered publications from March 2020 to April 2021. ​Studies mentioning biases on AI algorithms developed for contact (...) tracing and medical triage or risk prediction regarding COVID-19 were included. From 1054 identified articles, 20 studies were finally included. We propose a typology of biases identified in the literature based on bias, limitations and other ethical issues in both areas of analysis. Results on health disparities and SDOH were classified into five categories: racial disparities, biased data, socio-economic disparities, unequal accessibility and workforce, and information communication. SDOH needs to be considered in the clinical context, where they still seem underestimated. Epidemiological conditions depend on geographic location, so the use of local data in studies to develop international solutions may increase some biases. Gender bias was not specifically addressed in the articles included. The main biases are related to data collection and management. Ethical problems related to privacy, consent, and lack of regulation have been identified in contact tracing while some bias-related health inequalities have been highlighted. There is a need for further research focusing on SDOH and these specific AI apps. (shrink)

The main aim of this article is to reflect on the impact of biases related to artificial intelligence (AI) systems developed to tackle issues arising from the COVID-19 pandemic, with special focus on those developed for triage and risk prediction. A secondary aim is to review assessment tools that have been developed to prevent biases in AI systems. In addition, we provide a conceptual clarification for some terms related to biases in this particular context. We focus mainly on nonracial biases (...) that may be less considered when addressing biases in AI systems in the existing literature. In the manuscript, we found that the existence of bias in AI systems used for COVID-19 can result in algorithmic justice and that the legal frameworks and strategies developed to prevent the apparition of bias have failed to adequately consider social determinants of health. Finally, we make some recommendations on how to include more diverse professional profiles in order to develop AI systems that increase the epistemic diversity needed to tackle AI biases during the COVID-19 pandemic and beyond. (shrink)

The aim of this article is to know the role of learning tasks within the pedagogical content knowledge of novel sports coaches in initial stages of sports training of children/young people and their impact on their daily work. Participants are two coaches in their first or second working year. A mixed methodology was used by means of polar coordinates analysis. The results agree with previous studies that established that PCK of novel coaches presents deficits in task selection and modification, motivation (...) is the key factor determining tasks selection process, and they do not know how much time they should dedicate to each task. Even so, better development was found in the PCK of the coaches. (shrink)

BackgroundMonitoring recovery–stress balance in sport is becoming more relevant to prevent training maladaptation and reach the optimal performance for each athlete. The use of questionnaires that identify the athlete’s recovery–stress state have much acceptance in sports due to reliability and useful, furthermore for its low cost. Identifying possible differences between sport modalities and sex is important to determine specific needs and possible intervention ways to keep a recovery–stress balance. The aim was to analyze the differences in the recovery–stress state and (...) mood states by sex and sport type during the competitive phase in young Mexican athletes. As a secondary objective, the psychometric properties of the Mexican version of the Recovery–Stress Questionnaire for Athletes were analyzed.MethodsA cross-sectional study was carried on with 461 athletes, 17.95 years old, from six sports disciplines. The RESTQ-Sport and Profile of Mood States were applied in a single moment. Differences by sex and sports modality were analyzed. RESTQ-Sport’s confirmatory factor analysis was performed after the stress and recovery theoretical structure of two stress and two recovery dimensions, and last, the concurrent validation with the POMS was carried on.ResultsSignificant differences by sex were found in the General Recovery and Sport Stress dimensions of the RESTQ-Sport as well as Vigor factor of the POMS, being higher for men; furthermore, both the Sport Recovery dimension of RESTQ-Sport and Cholera and the Fatigue and Depression factors from POMS also had differences by sport type, showing a less recovery and high stress for individual sport athletes. Goodness-of-fit indexes of the model for the RESTQ-Sport were acceptable. Pearson’s correlation between questionnaires was moderate.ConclusionThe recovery–stress state shows differences in the function of sex and sport modality. More special attention is suggested for women and individual sport athletes. The higher punctuation for men compared with women in sport stress dimension did not negatively affect the recovery–stress balance for male athletes. Finally, the Mexican context adaptation of the RESTQ-Sport provides a psychometric instrument suitable to assess the recovery–stress balance in Mexican athletes. (shrink)

Over the past two decades the growth of the organic sector has been accompanied by a shift away from first party, or peer review, systems of certification and towards third party certification, in which a disinterested party is responsible for the development of organic standards and the verification of producer compliance. This paper explores some of the limitations of the third party certification model and presents the case of Mexico as an example of how an alternative form of participatory certification (...) has emerged. The paper suggests that participatory guarantee systems (PGS) are reflective of the growing “beyond organic” movement, which focuses on reconstructing the local and re-embedding food systems into their socio-ecological contexts. It argues that PGS offers a number of benefits for producers and consumers, particularly in the South, but that it faces a number of challenges as well, such as a lack of formal recognition, social conflicts and dependence on donated resources. (shrink)

Introducción: los accidentes son de las primeras causas de muerte a nivel mundial, por lo que la prevención de los mismos es una emergencia. Objetivo: valorar la repercusión de una intervención comunitaria en la disminución de peligros potenciales de accidentes en familias con niños de 0 a 18 meses. Métodos: se realizó un estudio cuasi experimental multietápico, con enfoques cuantitativo y cualitativo, entre enero de 2009 a junio de 2012. Se trabajó con 39 familias entre las que se produjeron nacimientos (...) en el periodo enero de 2008 a enero de 2010 de los Consultorios Médicos del Consejo Popular 26 de julio del Municipio Santo Domingo. Se efectuó una intervención por un grupo de trabajo comunitario conformado por integrantes del Círculo de interés "Prevención es Salud" y brigadistas de la Cruz Roja, liderados por la enfermera de la familia, se empleó para ello la Guía para Análisis de vulnerabilidades y capacidades de la Cruz Roja, modificada en su etapa I. Resultados: Post intervención se logró la reversión de vulnerabilidades en cuanto a capacidades, se manifestaron cambios favorables en los conocimientos y disminuyó significativamente el número de peligros potenciales en cada hogar. Conclusiones: Cuando se trabaja con familias con instrumentos sencillos y accesibles, y con el grupo de trabajo comunitario, se favorece la toma de conciencia sobre el problema en el entorno donde se generó. Introduction: accidents are one of the first causes of death worldwide, so their prevention is an urgency. Objective: assess the effect of a community intervention in the reduction of potential dangers of accidents in family with children aged from zero to 18 months. Methods: a multiage cuasi experimental study was carried out, with quantitative and qualitative approaches, from January 2009 to June 2012. The sample was taken from thirty-nine families who had children in the period ranging from January 2008 to January 2010 belonging to the family doctor´s house of the community called "26 de Julio" from Santo Domingo municipality. An intervention was carried out by a community group work composed by members of centers of interests called ¨Prevention is health¨ and members of the Red Cross led by the family nurse. It was necessary to ask a guide to analyze the vulnerabilities and capabilities of the Red Cross, modified in the first stage. Results: During the post intervention, it was possible to change the vulnerabilities in terms of capacities, favorable changes were present in the knowledge and the number of potential risks significantly decreased in each house. Conclusions: when families are approached with simple and accessible instruments, and with a community group work it is possible to make favorable changes in terms of awareness of the problem in the same place where it emerged. (shrink)

The author settles down a point of union between the philosophy of Plotino and the poetry that in honour to San Juan de la Cruz she published in the work Aunque haya niebla. In this poem's book she tries herself to see God without falling in the pantheism.

En este artículo el profesor Manuel Ángel Martínez expone los temas más importantes de la reflexión teológica de Antonio Royo Marín. Se centra especialmente en una de sus obras más importantes La Teología de la Perfección. Royo Marín ha sido un predicador infatigable. Muestra de ello son los numerosos escritos que dejó y su amplia divulgación entre muchos fieles cristianos. Varios grupos, repartidos en diversos lugares del mundo, siguen nutriéndose de su teología. La profundidad con la que están escritos y (...) la claridad de su exposición permiten a muchos lectores un acercamiento a la espiritualidad cristiana y a sus fuentes. Los Santos Padres de los primeros siglos del cristianismo, Santo Tomás, Santa Teresa de Jesús, San Juan de la Cruz, Santa Teresa de Lisieux, Santa Catalina de Siena, Juan González Arintero, entre otros, inspiraron la reflexión teológica de Royo Marín.El 17 de abril se cumplirán cinco años de su fallecimiento. Con este motivo y respondiendo a las numerosas demandas que nos han llegado, ofrecemos a todos los lectores la magnífica descripción que de su teología ha escrito en Ciencia Tomista el profesor Manuel Ángel Martínez Juan. (shrink)

En este artículo el profesor Manuel Ángel Martínez expone los temas más importantes de la reflexión teológica de Antonio Royo Marín. Se centra especialmente en una de sus obras más importantes La Teología de la Perfección. Royo Marín ha sido un predicador infatigable. Muestra de ello son los numerosos escritos que dejó y su amplia divulgación entre muchos fieles cristianos. Varios grupos, repartidos en diversos lugares del mundo, siguen nutriéndose de su teología. La profundidad con la que están escritos y (...) la claridad de su exposición permiten a muchos lectores un acercamiento a la espiritualidad cristiana y a sus fuentes. Los Santos Padres de los primeros siglos del cristianismo, Santo Tomás, Santa Teresa de Jesús, San Juan de la Cruz, Santa Teresa de Lisieux, Santa Catalina de Siena, Juan González Arintero, entre otros, inspiraron la reflexión teológica de Royo Marín.El 17 de abril se cumplirán cinco años de su fallecimiento. Con este motivo y respondiendo a las numerosas demandas que nos han llegado, ofrecemos a todos los lectores la magnífica descripción que de su teología ha escrito en Ciencia Tomista el profesor Manuel Ángel Martínez Juan. (shrink)

Unamuno and Ganivet approach the historical fact from romanticism (Ranke and Humboldt), as well as from hegelianism, whose original bond is "Volkgeist". More exactly, the Ganivet's concept of "spirit of the territory" is influenced by Hipólito Taine and Unamuno's concept of "intrahistory" by Spencer. The historical knowledge is leaded by a dialectic between the individual and the universal, similar to dialectic between superficial and deep.

The purpose of this work is to analyze the concept of «critical interculturality» and to explore the way in which an appropriate ethics could be defined. To this end, I will raise the problem of cultural diversity and make a brief tour of some of the socio-political forms with which it has been managed in the last half century, mainly in egalitarian liberalism. Against this distinctly Anglo-American perspective, I will oppose a geographically and/ or epistemically situated approach in the Americas. (...) Along the path, I will underline the notions that could backbone a critical intercultural ethics, among which I will highlight, within the framework of an intercultural philosophy, dialogue and cultural recognition. (shrink)

Individuals and businesses make numerous payments every day. They sometimes have choices about what forms of payment to make or accept, and at other times are effectively forced to use a particular form. Often there is an asymmetric power relationship between payer and payee that raises the issue of whether one side unfairly exploits the other. Is it unethical exploitation for an employer to pay employees with a fee-laden payroll card over other more convenient forms of payment? Does the fee (...) structure of payment networks such as Visa and MasterCard unfairly exploit merchants? The bitcoin payment system is an ethical as well as technological evolution as it was designed to be an electronic payment system that does not rely upon trust. Can an entire payment system like bitcoin be “evil,” as charged by Krugman? Payment tools as such are ethically neutral, but can be used in an ethical or unethical manner. (shrink)

El análisis que se desarrolla en este artículo, está dirigido a desconstruir el modelo de episteme de la racionalidadmoderna, que tiene por pretensión la reconstrucción objetiva de la realidad y su validez universal y absoluta para cualquier contexto cognitivo. Se propone una alternativa a este tipo..

In this paper we show that, in Gentzen systems, there is a close relation between two of the main characters in algebraic logic and proof theory respectively: protoalgebraicity and the cut rule. We give certain conditions under which a Gentzen system is protoalgebraic if and only if it possesses the cut rule. To obtain this equivalence, we limit our discussion to what we call regular sequent calculi, which are those comprising some of the structural rules and some logical rules, in (...) a sense we make precise. We note that this restricted set of rules includes all the usual rules in the literature. We also stress the difference between the case of two-sided sequents and the case of many-sided sequents, in which more conditions are needed. (shrink)

Si Michel Henry ha reclamado para su filosofía el título de “fenomenología material”, ello se debe a un intento por desentrañar la “substancia fenomenológica invisible” del aparecer en tanto la inmediación patética en la cual la vida se experimenta a sí misma. Si dicho auto-aparecer de la vida consiste en la “unidad no tautológica” del “sufrir” en tanto la pasividad originaria a sí mismo y el “gozo” en tanto la efectuación en la que el sentirse se lleva a cabo, proponemos (...) reinterpretar dicha unidad a partir de una “estructura antinómica”. Así, si el sufrimiento designa la excedencia de la pasividad originaria en tanto “imposibilidad”, el gozo debe ser entendido en tanto la excedencia de una “transpasibilidad”. Dicho sobrepasamiento tiene como consecuencia el que la “hiper-potencia” se traduzca en una “hiper-contingencia” en un doble sentido. Por un lado, como la contingencia de todo pretendido “estar-en-posesión-de-sí”, incluido el del fenomenólogo mismo, es decir, como la “transgresión” de su propia arquitectónica. Por otro lado, si dicha contingencia aspira a sobrepasar todo “monismo ontológico”, entonces solo puede tener lugar en tanto “con-tagio”, es decir, en tanto una sobreabundancia de “con-tactos”. (shrink)

Low‐back pain can be invalidating physically as well as mentally. Despite professional help to treat and prevent low‐back pain, the pain often persists, and so do the problems related to low‐back pain. An intervention that made it possible for a significant part of patients with low‐back pain to improve health and well‐being raised the question: Why was it possible to help some and not others? The aim of the present paper was to achieve a deeper understanding of factors patients experienced (...) as helpful in professional support related to low‐back pain. This was explored using a hermeneutic‐phenomenological approach while analysing 20 interviews with patients with low‐back pain purposively chosen interviews conducted in relation to the intervention. An analysis was made using Ricoeur's interpretation theory. Data on both positive and negative experiences were read and reflected upon. We found that healthcare professionals’ adoption of a narrative approach facilitating the patient's perspective was perceived as helpful. Patients experienced this as being taken seriously; an experience that could be explained at a deeper, more nuanced level using Heidegger's philosophy. Facilitating the patient's perspective was conditional not only on the professional obtaining access to the patient's perspective but also on understanding and acknowledging the patient's existence. The challenge for healthcare professionals in this respect is to bridge the gap between the consultation's fact‐focused concern with the medical implications of low‐back pain and the patient's concern with the implications low‐back pain has for his or her personal identity and life. Listening to the patient's perspective in itself supports the subjective recovery process, while also supporting the quality of patient‐centred support and strengthening the patient's trust in its helpfulness. (shrink)

Theoria, Volume 87, Issue 4, Page 971-985, August 2021.

Desde la tradicional linealidad temporal hasta la temporalización estética y premeditadamente elaborada, se estudian aquí los diferentes enfoques de la temporalidad en la novela mexicana desde Al filo del agua de Agustín Yáñez hasta La ley del amor de Laura Esquivel, pasando por Pedro Páramo de Juan Rulfo, La muerte de Artemio Cruz de Carlos Fuentes, Palinuro de México de Fernando del Paso y Arráncame la vida de Ángeles Mastretta.

Recently there has been an outpouring of consumer frustration over rising food and energy prices. Many politicians railed against “speculators” who allegedly drove up the prices of key necessities. Is speculation unethical? This article reviews the traditional arguments against speculation. Many of the standard criticisms confuse speculation with gambling. In much the same way as ethicists now draw distinctions between usury and normal business interest, we draw a distinction between socially useful speculation and gambling. Gambling involves taking on risk with (...) no plausible expectation of making a profit. Gambling may provide entertainment value to some people, but like other addictive activities causes grave harm to a subset of users. Speculation involves taking on a business risk with a plausible expectation that a profit will result. Speculators provide an important risk bearing service by taking on risks that others do not want. They help markets to function better by helping to incorporate information into prices as well as providing liquidity. Speculators may actually reduce shortages by causing quicker price increases that motivate producers to increase production and consumers to conserve. But even socially useful speculation may have an ethical dark side. Does such speculation cause damage by adding excess volatility to prices? Speculators may contribute to price bubbles. At what point does legitimate speculation become odious “price gouging?” We also draw an ethical distinction between speculation, which seeks to benefit from changing prices, and manipulation, actions taken to push prices away from their economically appropriate levels. (shrink)

La terminología más exacta para hablar de los derechos del hombre, es la de ser «fundamentales», porque afectan a las dimensiones más básicas del ser humano y,por ello mismo, tienen que ser protegidos y garantizados por los poderes públicos. Se trata de derechos públicos subjetivos que son universales, imprescriptibles, irrenunciables e inalienables. Tienen límites filosóficos, de naturaleza sociológica o por razón de su finalidad. Poseen un fundamento iusnaturalista y no meramente positivista. Las primeras declaraciones de derechos fundamentales universales no aparecen (...) hasta finales del siglo XVIII, con carácter de individuales y personales, para, después, incorporar también derechos sociales, económicos, culturales y a los actuales de protección del medio ambiente, minusválidos, etc. Es lo propio del actual Estado social y democrático de derecho. (shrink)

A model of Zeno's dichotomy paradox is presented in Newtonian collision mechanics. One of several resolutions of the paradox illustrates the point that even in Newtonian ontology there is a spacetime weave. In a Newtonian system in which the base rules permit only spatial contact interactions, we find the mechanical emergence of action-at-a-distance effects.

La presente ponencia se origina a partir de la siguiente pregunta: ¿«raza» (Rasse) y «sexo» (Geschlecht) son conceptos bajo los cuales es posible hallar una filosofía latente del cuerpo en Heidegger? En cuanto concierne al concepto de «raza», es patente el carácter ambiguo de dicha pregunta, si se toma en consideración la recepción que han tenido los Cuadernos negros, a saber, como el material a partir del cual cabría determinar hasta qué punto el antisemitismo «contaminaría» la filosofía de Heidegger. Y (...) ello porque la aproximación heideggeriana al concepto de lo «racial» (rassisch) consistirá precisamente en rechazar toda comprensión naturalista o biológica para transponerla de manera digamos «ontológica» en el concepto de lo «de buena casta» (rassig), el cual está fundamentado en el «ser-arrojado» (Geworfenheit) como constituyente del «pueblo» (Volk) en su carácter historial. Por otro lado, es de común acuerdo el carácter problemático tanto de la corporalidad como de la espacialidad en la ontología heideggeriana, en tanto parece otorgárseles un lugar meramente «óntico» que debe ser reconducido asimismo de manera ontológica al «corporar» (leiben) codeterminante del «ser-en-el-mundo». Dicha aproximación a la corporalidad, por ejemplo, en los Seminarios de Zollikon, que consiste en calificarla de «condición necesaria pero no suficiente», es la misma que caracteriza su posición crítica con respecto a la «raza», la cual consistiría en el gesto impropio de elevar «una condición al estatuto de lo incondicionado». Dicho gesto mostrará su aporía en tanto debe al mismo tiempo expulsar fuera de sí un «resto»: en el caso de la raza, un pueblo que rehúsa su carácter de «pueblo». Finalmente, se abordará un intento de pensar la «raza» en su materialidad a través del concepto de «mestizaje». (shrink)

Como afirma Roland Vaschalde en Suivant Michel Henry (2022), el título se sirve de la expresión «siguiendo a» (suivant) tanto con el sentido de «según» como con el de «como se sigue de», con lo cual no pretende «repetir» a Henry, sino asimismo prolongar los horizontes de la fenomenología de la praxis viviente. Si, de acuerdo con la tópica henriana, dicho «seguir» en tanto uno de los haceres propios a mi «yo puedo» se funda en una «persecución», es decir, en (...) un «sufrirse» ya sea en la imposibilidad de apropiarse del otro, ya sea en tanto sentirse «perseguido», es decir, hallarse bajo la dominación del otro en la imposibilidad de liberarse del peso de mi propio yo, el cual a su vez se «goza» en el olvido de dicha imposibilidad en la ilusión trascendental de su «consecución» en tanto la coincidencia de mi yo con la vida, lo que queda por pensar es la posibilidad del «proseguir» en tanto la transformación de la propia topología. Y es dicho «proseguir» el cual impulsará nuestra lectura a través de las figuras de lo onírico, de lo poscolonial, de la psicopatología, del judaísmo y de la cartografía del cuerpo, en tanto lo «imperseguible» de la fenomenología henriana. (shrink)

El presente texto constituye, por un lado, una continuación de una aproximación materialista al concepto de “raza” a partir de los Cuadernos negros de Heidegger, la cual nos llevó, luego de reconocer su carácter análogo a la “corporalidad”, a pensarla no como una determinación naturalista o biológica, sino como la posibilidad de un “mestizaje ontológico”. Por otro lado, “sexo”, “estirpe” y “estilo” hacen alusión a la polisemia del concepto de “Geschlecht” como una figura de lo que hemos llamado la ambigüedad (...) fenomenológica del eros en términos de una “prohibición y transgresión arquitectónicas”. Ello se traducirá, por un lado, en la prioridad del “estilo” como reunión del decir poético en lo impronunciado del poema, y no, como propondremos, en la “excripción” de una “transposición metonímica”, y, por otro lado, en el silenciamiento por Heidegger de la figura del “incesto” en la poesía de Trakl. (shrink)

¿Cómo hacer un resumen de un escrito que problematiza el propio concepto de «sumilla»? En primer lugar, señalamos el carácter problemático de la sumilla, entendida como la pretensión de traer a presencia la ponencia y al mismo tiempo de postergarla. En segundo lugar, mostramos cómo en el proceder dialógico platónico acontece dicho carácter problemático de la presencia (eîdos) en términos del continuado fracaso respecto de todo intento de fijación del ser del ente, es decir, de su constante postergación. Más aún, (...) afirmamos que la pretensión meta-dialógica del diálogo platónico, es decir, de dar cuenta de aquello que en el diálogo mismo acontece, tiene lugar en términos de una toma de distancia respecto de su propio carácter escrito. En tercer lugar, escenificamos dicho carácter meta-dialógico mediante un tramo del Parménides, en el cual dicha toma de distancia asume la forma de la historia del robo del escrito de Zenón, lo cual quiere expresar que el eîdos no tiene lugar sino en su propio ausentarse. Y es que, en efecto, esto no habrá sido sino un resumen si remitimos al resumere latino, es decir, al re-asumir, a su vez reasunción del analambánein griego. Es precisamente dicho analambánein el que Platón liga con la anámnesis, es decir, con la reminiscencia, la cual a su vez remite a una ausencia constituyente. (shrink)

From the development of Literature Theory wich based on the analogy with Architecture the author analyze the relationships between Cervantes and Vargas Llosa works. Research on Cervantes reception in Latin America it is a work to keep doing. In Peru Vargas Llosa has received Cervantes works in a peculiar way. This paper tries to clarify what are the structural relations between these two literary architecture.

ABSTRACT In this paper we study consequence relations on the set of many sided sequents over a propositional language. We deal with the consequence relations axiomatized by the sequent calculi defined in [2] and associated with arbitrary finite algebras. These consequence relations are examples of what we call Gentzen systems. We define a semantics for these systems and prove a Strong Completeness Theorem, which is an extension of the Completeness Theorem for provable sequents stated in [2]. For the special case (...) of the finite linear MV-algebras, the Strong Completeness Theorem was proved in [10], as a consequence of McNaughton's Theorem. The main tool to prove this result for arbitrary algebras is the deduction-detachment theorem for Gentzen systems. (shrink)