public CTLFormula(CTLExpressionType type, CTLFormula left, CTLFormula right)
 {
     Type         = type;
     LeftFormula  = left;
     RightFormula = right;
 }
 public CTLFormula(CTLExpressionType type, string lexeme)
 {
     Type   = type;
     Lexeme = lexeme;
 }
 public CTLFormula(CTLExpressionType type, CTLFormula left)
 {
     Type        = type;
     LeftFormula = left;
 }
 public CTLFormula(CTLExpressionType type)
 {
     Type = type;
 }