subst this
l : List Char
it : Iterator
h : ¬it.atEnd = true
c : Char
r' : List Char
v : ValidFor l (c :: r') it
this✝ : ¬c :: r' = []
this : it.curr = c
⊢ ∃ r'_1, c :: r' = it.curr :: r'_1
l : List Char
it : Iterator
h : ¬it.atEnd = true
r' : List Char
v : ValidFor l (it.curr :: r') it
this : ¬it.curr :: r' = []
⊢ ∃ r'_1, it.curr :: r' = it.curr :: r'_1