We see the defining properties of constructive mathematics as being the proof interpretation of the logical connectives and the definition of function as rule or method. We sketch the development of intuitionist type theory as an alternative to set theory. We note that the axiom of choice is constructively valid for types, but not for sets. We see the theory of types, in which proofs are directly algorithmic, as a more natural setting for constructive mathematics than set theories like IZF. (...) Church’s thesis provides an objective definition of effective computability. It cannot be proved mathematically because it is a conjecture about what kinds of mechanisms are physically possible, for which we have scientific evidence but not proof. We consider the idea of free choice sequences and argue that they do not undermine Church’s Thesis. (shrink)

What is the definition of 'type'? Having a clear and precise answer to this question would avoid many misunderstandings and prevent meaningless discussions that arise from them. But having such clear and precise answer to this question would also hurt science, "hamper the growth of knowledge" and "deflect the course of investigation into narrow channels of things already understood". In this essay, I argue that not everything we work with needs to be precisely defined. There are many definitions used by (...) different communities, but none of them applies universally. A brief excursion into philosophy of science shows that this is not just tolerable, but necessary for progress. Philosophy also suggests how we can think about this imprecise notion of type. (shrink)

I give a concise description of my personal view on symbolic computation, its place within mathematics and its relation to algebra. This view is exemplified by a recent result from my own research: a new symbolic solution method for linear two-point boundary value problems. The essential features of this method are discussed with regard to a potentially novel line of research in symbolic computation.