simp
case cons
df : DagFormula
head✝ : Program
tail✝ : List Program
⊢ undagDagFormula (⌈⌈head✝ :: tail✝⌉⌉df) = ⌈⌈head✝ :: tail✝⌉⌉undag df
case cons
df : DagFormula
head✝ : Program
tail✝ : List Program
⊢ undagDagFormula (⌈⌈tail✝⌉⌉df) = ⌈⌈tail✝⌉⌉undagDagFormula df