Function embeds 

pub fn embeds<'a>(e1: &Expr<'a>, e2: &Expr<'a>) -> bool

Homeomorphic embedding check: e1 ◁ e2.

Returns true if e1 is homeomorphically embedded in e2, meaning e1 can be obtained from e2 by erasing some constructors (diving) or both share the same constructor with all children embedded (coupling).