An edge's call, once its target is known: the call itself when the step's
input I is the target's input, else a type that names the mismatch — so a
wrong input is a type error where the edge is used, without the declaration
depending on the target's type.
An edge's call, once its target is known: the call itself when the step's input
Iis the target's input, else a type that names the mismatch — so a wrong input is a type error where the edge is used, without the declaration depending on the target's type.