SUBLET_CONV : conv -> term -> thm
let v1 = t1 and ... and vn = tn in t
|- (let v1 = t1 and ... and vn = tn in t) = (let v1 = t1' and ... and vn = tn' in t) where applying conv to ti results in the theorem |- ti = ti'.
# SUBLET_CONV NUM_ADD_CONV `let x = 5 + 2 and y = 8 + 17 and z = 3 + 7 in x + y + z`;; val it : thm = |- (let x = 5 + 2 and y = 8 + 17 and z = 3 + 7 in x + y + z) = (let x = 7 and y = 25 and z = 10 in x + y + z)