/// <summary>
        /// Create a probe that evaluates to "true" when the value returned by <paramref name="p1"/>
        /// is less than the value returned by <paramref name="p2"/>
        /// </summary>
        public Probe Lt(Probe p1, Probe p2)
        {
            Contract.Requires(p1 != null);
            Contract.Requires(p2 != null);
            Contract.Ensures(Contract.Result<Probe>() != null);

            CheckContextMatch(p1);
            CheckContextMatch(p2);
            return new Probe(this, Native.Z3_probe_lt(nCtx, p1.NativeObject, p2.NativeObject));
        }

        /// <summary>
        /// Create a tactic that fails if the probe <paramref name="p"/> evaluates to false.
        /// </summary>
        public Tactic FailIf(Probe p)
        {
            Contract.Requires(p != null);
            Contract.Ensures(Contract.Result<Tactic>() != null);

            CheckContextMatch(p);
            return new Tactic(this, Native.Z3_tactic_fail_if(nCtx, p.NativeObject));
        }

        /// <summary>
        /// Create a tactic that applies <paramref name="t"/> to a given goal if the probe 
        /// <paramref name="p"/> evaluates to true. 
        /// </summary>
        /// <remarks>
        /// If <paramref name="p"/> evaluates to false, then the new tactic behaves like the <c>skip</c> tactic. 
        /// </remarks>
        public Tactic When(Probe p, Tactic t)
        {
            Contract.Requires(p != null);
            Contract.Requires(t != null);
            Contract.Ensures(Contract.Result<Tactic>() != null);

            CheckContextMatch(t);
            CheckContextMatch(p);
            return new Tactic(this, Native.Z3_tactic_when(nCtx, p.NativeObject, t.NativeObject));
        }

        /// <summary>
        /// Create a tactic that applies <paramref name="t1"/> to a given goal if the probe 
        /// <paramref name="p"/> evaluates to true and <paramref name="t2"/> otherwise.
        /// </summary>
        public Tactic Cond(Probe p, Tactic t1, Tactic t2)
        {
            Contract.Requires(p != null);
            Contract.Requires(t1 != null);
            Contract.Requires(t2 != null);
            Contract.Ensures(Contract.Result<Tactic>() != null);

            CheckContextMatch(p);
            CheckContextMatch(t1);
            CheckContextMatch(t2);
            return new Tactic(this, Native.Z3_tactic_cond(nCtx, p.NativeObject, t1.NativeObject, t2.NativeObject));
        }

        /// <summary>
        /// Create a probe that evaluates to "true" when the value <paramref name="p"/>
        /// does not evaluate to "true".
        /// </summary>
        public Probe Not(Probe p)
        {
            Contract.Requires(p != null);
            Contract.Ensures(Contract.Result<Probe>() != null);

            CheckContextMatch(p);
            return new Probe(this, Native.Z3_probe_not(nCtx, p.NativeObject));
        }