Exercise: a's, followed by b's, followed by c's followed by d's with an equal number of a's and c's or b's and d's

Use the pda applet below to construct a PDA that accepts strings of the form

{ $a^i{b}^j{c}^k{d}^m$ | i = k or j = m, and i, j, k, m ≥ 0 }

Examples of strings to accept	Examples of strings to reject
ε ac bd abcd aabcc bbbcccddd bbd b	abbd abbccddd abacd bbcd aabbbcccdd bc

 

 

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Copyright © Rockford J. Ross 1991-2007