Thank you, Grouchy Chris. This settles the matter to a great extent, at least for me, since I am used to the old 3rd. edition maneuver.
Yet, just for the sake of curiosity, I would like to find a raw solution for the two situations:
1) Warrior A closing in a foe B in a three yard wide dead-end alley, and;
2) The "Slicing the Pie" situation (GURPS Tactical Shooting, p. 24).
The best I could devise was using Wait maneuver triggered by a clause "If nothing happens in a heartbeat, I Step and (keep) Ready my weapon".
In the case of the situation #2, a guy with a gun would declare a series of Wait maneuvers like that: "If I don't see anything coming from that corner during a heartbeat, I will Step and (keep) Ready my Rifle".
Situation #1 seems more tricky. Fourth edition Wait maneuver likes Link magic (Magic, p.134), because it is strict and once set cannot be changed. So, if warrior A and B were two players instead of PC and NPC, they should write down their "If clauses", or whisper them in the GM's ears.
In this hypothetical situation, Warrior A controls the exit of a three yard wide alley, and do not wish foe B to escape. He would begin with Wait maneuvers triggered this way: "if foe b falls within my sword reach, I will slice him" (Warrior's Clause 1). That would generate a stalemate situation, because player B could declare "I do nothing" (Foe's Clause), and this situation repeats for, say, 20 turns.
Then, Warrior A could secretly change his triggering condition in one turn to "If foe B doesn't move in a heartbeat, I will Step and Ready" (Warrior's Clause 2). In his next turn, which comes immediately after, he would return to the "if foe by falls within my sword reach..." thing.
Foe B could risk to run in his own turn, but he would never know for sure if Warrior A was "programmed" for walking or striking that very second. It would be a matter of risking and taking the opportunity, but he could have the chance of passing by him. This could be fun, for two reasons. First, it generates some suspense, what is great. Second, the faster a Warrior tries to encroach his opponent, the bigger his risks.
In the case of an NPC, a GM could either write down the Wait conditions in secret, and play it like a poker game, or he could only ask the player for its rate of alternation - like, each 10 seconds of Warrior's Clause 1, I will risk a Warrior's Clause 2, and roll a die for, say 10%. Or, if a foe rolls an Acting test, he could lead the Warrior to think he really means to surrender himself, only to slip through his fingers.
If the warrior has more than five minutes, this stalemate situation could be ignored. But if he is in a hurry, this would simulate realistic hesitation. A Warrior would have to really inch forward if wanted to make things the safe way. Otherwise, he would be trading haste for waste.
Kromm
here says that a Wait clause can be complex, but cannot be vague. In raw, am I allowed say "if nothing happens during a turn (or a heartbeat), I will do the following"?