A correctness check must be done for each expression. A such expression must contain only the dependent variables, some numbers (integers or floating point numbers), the arithmetic operators
and the mathematical functions
In the solution computation process these expressions must be evaluated. A very simple way to do these tasks is to transform each mathematical expression in its equivalent Polish sequence (for example, by the operators pile technique), and, giving the current values of the dependent variables, to evaluate the Polish sequence (for example to exp((a+b)*c+ln(10*e))/5 corresponds ab+c*10e*ln+exp5/) .