is mentioned by

Thm* x:Label, r:rel(). (x rel_vars(r)) (i:. i < ||r.args|| & (x term_vars(r.args[i])))	[member_rel_vars]
Thm* a,b:Term List. a = b ||a|| = ||b|| (i:. i < ||a|| & a[i] = b[i])	[unequal_termlists]
Def rel_mentions(r;x) == i:. i < ||r.args|| & (x term_vars(r.args[i]))	[rel_mentions]

In prior sections: mb basic mb list 1 mb collection

Try larger context: GenAutomata