Rule for Connectives I: for /\: "If φ[n-m] and ψ[n-l] are formulae, φ /\n ψ is a formula"

Rule for Connectives

I:

for /\:

"If

φ_[n-m] and ψ_[n-l] are formulae,

φ /\_n ψ

is a formula"