Your contractor from Elbonia has sent you the prototype of the new logical unit. It turns out that the only logical relation it understands is "nand":
nand(a,b) := ~(a&b)
Your team has been developing code using the usual logical operators following MATLAB syntax: ~,& and |. To save the project you need to write a translator that expresses MATLAB logical expressions using only the nand function.
expr = 'a|(~b)' =>out = 'nand(nand(a,a),b)'
expr = '(a & ~a) | ~(a|b)' =>out = 'nand(nand(nand(a,a),nand(b,b)),nand(nand(a,a),nand(b,b)))'
It is not necessary to provide the shortest solution. A solution always exists. The input string is non-empty and always evaluates to true or false, if a and b are logical variables. All substrings in the output that are not 'a','b','0','1','true','false','(',')' or'nand' will be ignored.