aⁿbⁿcⁿdⁿ using 2-stack PDA
Check out this link: https://stackoverflow.com/questions/40317006/pushdown-automaton-pda-for-l-anbncnn-1#= or check the answer below.

2 stack PDA to recognize the language {an bn cn dn n>=0} for this we should follow the given steps:

Use the first stack for checking an bn, this can be done by pushing a whenever you see an a and then popping a when you see a b.

Use the second stack for checking bn cn  this can be done by pushing b whenever you see a b and then popping b when you see a c.

Use the first stack for checking cn dn  this can be done by pushing c whenever you see a c and then popping c when you see a d.

Accept if both stacks are empty at the end of this process, otherwise do not accept it.

Let ^ and z be the stack symbol of stack 1 and 2 respectively, then the transition diagram of the above PDA will be as follows: