9 Nov
1998
9 Nov
'98
9:31 p.m.
Philippe Gaucher <gaucher@irma.u-strasbg.fr> asked:
for a CPS, is there a way to compute the source and target of a R({x}) using only compositions of elements like R({y}) ?
Yes and no. Yes in the sense that because the source and the target are pasting schemes themselves, Johnson's pasting theorem gives that 1. they are compositions of R({y})'s and 2. *any* way you do this gives the same result. No in two senses: although Johnson's proof actually gives an algorithm, I don't think this algorithm has ever been implemented (in AXIOM for example); and secondly, there is (as far as I know) no *general* expression which works for cubes of all dimensions. Sjoerd Crans