Module type Substitution.Substituable


module type Substituable = sig .. end

type variable 
The type of variables.
type term 
The type of terms, i.e. of things we want to substitute variables with.
type substituable 
The type of a substituable object, would it be an index, a schema or other.
val substitute : substituable ->
var:variable ->
by:term -> substituable
The substitution function. Substitutes var by by in a substituable data.