--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Prover/Contexts.pizza	Thu Mar 15 10:07:28 2012 +0000
@@ -0,0 +1,70 @@
+package G4ip;
+
+import java.util.Vector;
+import G4ip.Form.*;
+
+/** Context acts as a multiset.<p>
+  * Typical contexts in logical rules are Gamma, Delta, etc.
+  * @author      Christian Urban
+  */
+public class Context extends Vector {
+  
+  public Context() { super(); }
+
+  public Context(Context init_context) {
+    super();
+    for (int i=0;i<init_context.size();i++) {
+      addElement(init_context.elementAt(i));
+    }
+  }
+
+  /** should be toString, but this is a "final" method in Vector 
+    */
+  public String makeString() {
+    String s = new String();
+    int i;                      // size()-1 because the last formula
+    for (i=0;i<size()-1;i++) {  // should be printed without a comma
+      s=s.concat(elementAt(i).toString());
+      s=s.concat(", ");
+    }
+    if (size() > 0) {           // add last formula 
+      s=s.concat(elementAt(i).toString()); 
+    }
+    return s;
+  }
+
+  /** returns a context with one additional formula at the beginning 
+    * @param   new_formula    a formula
+    */
+  public Context add(Form new_formula) {
+    Context new_c = new Context(this);
+    new_c.insertElementAt(new_formula,0);
+    return new_c;
+  }
+
+  /** returns a context with two additional formulae at the beginning 
+    * @param new_formula1,new_formula2    two formulae
+    */
+  public Context add(Form new_formula1, Form new_formula2) {
+    Context new_c = new Context(this);
+    new_c.insertElementAt(new_formula1,0);
+    new_c.insertElementAt(new_formula2,0);
+    return new_c;
+  }
+
+  /** tests whether a context contains a specific atom 
+    * @param a a formula
+    */
+  public boolean includes(Form a) {
+    if (a instanceof Atm) {
+      for (int i=0;i<size();i++) {
+        switch((Form)elementAt(i)) {
+        case Atm(String c):
+          if (c.compareTo(((Atm)a).c) == 0) return true; break;
+        }
+      }
+    }
+    return false;
+  }
+
+}