If the expression represents a single quote character (for a string or a literal), you should provide two single quotes for each single quote.
EvalStr('A' & 'B',' ') = 'AB'
If strings are not surrounded by quotes, they are regarded as variable references:
EvalStr(A & B,' ') = variable A and variable B.
Although using the variable letter codes is legal, it is best to avoid referring to variables by their codes because their location may vary.
If you wish to refer to variables, it is better to refer to them by their names using the VarCurrN and VarIndex functions. For example:
EvalStr('VarCurrN('NAME') and VarCurrN('LAST_NAME')',0)