# Fixes propagation of zero into known non-zero variable

Fixes #7 (closed)

It could append that we solve `1=xy`

by `x=y^-1`

because we know that `y\not=0`

but we later solve `y=0`

by the subtitution `y\mapsto 0`

. There is of course a contradiction but the order of the propagation can makes that it is the application of the substitution that finds it.