∑why 2 pda's....one is enough to solve it..yes it is practical...we can write code for it
∑ = (a,b) z= stack symbol F = q3
≰(q1, a, z) = (q1, az)
≰(q1, b, z) = (q1, bz)
≰(q1, a, b) = (q1, ab)
≰(q1, b, a) = (q1, ba)
≰(q1, a, a) = (q1, aa)
≰(q1, b, b) = (q1, bb)
for middle guess
≰(q1, ⋋, a) = (q2, a)
≰(q1, c, b) = (q2, b)
now to match and pop out
≰(q2, a, a) = (q2, ⋋)
≰(q2, b, b) = (q2, ⋋)
≰(q2, ⋋, z) = (q3, z)