More efficient implementation for substitutions.
More efficient implementation for substitutions.

We use a variant of skewed lists enriched over a monoid, whose purpose is
to count the number of lifts added to the substitution. This makes addition
O(1) and lookup O(log n).

SkySkimmer/coq,coq/coq,Zimmi48/coq,Zimmi48/coq,SkySkimmer/coq,silene/coq,JasonGross/coq,coq/coq,ejgallego/coq,coq/coq,coq/coq,Zimmi48/coq,SkySkimmer/coq,silene/coq,ejgallego/coq,silene/coq,JasonGross/coq,Zimmi48/coq,JasonGross/coq,ejgallego/coq,ejgallego/coq,JasonGross/coq,SkySkimmer/coq