public WS1SExists(String variable, WS1SFormula phi)
 {
     this.phi      = phi;
     this.variable = variable;
 }
 public WS1SNot(WS1SFormula phi)
 {
     this.phi = phi;
 }
 public WS1SOr(WS1SFormula left, WS1SFormula right)
 {
     this.left  = left;
     this.right = right;
 }
 public WS1SExists(String variable, WS1SFormula phi)
 {
     this.phi = phi;
     this.variable = variable;
 }
 public WS1SNot(WS1SFormula phi)
 {
     this.phi = phi;
 }
 public WS1SOr(WS1SFormula left, WS1SFormula right)
 {
     this.left = left;
     this.right = right;
 }