Spellweaver Helix infinite triggers?

[Hi-Val]

Say I've got two spellweaver helixes out imprinted with the same two sorceries. I cast a spell that triggers it, the helixes place two copies on the stack and then trigger again when they see eachother playing the copy, right? The stack would look like:

Trigger spell A
Helix Spell B
Helix Spell B
Helix Spell A
Helix Spell A
Helix Spell B
...

Right? How would one stop this?

Also, does Regrowth HAVE to target something or else it fizzles?

Thanks, O rules gurus!

[Jacob Orlove]

Spellweaver helix triggers when one of the sorceries is played, but it merely puts a copy on the stack, like how storm works.

If a spell targets, you can't play it without a legal targets. If that target is removed, the spell is countered on resolution.

[goober]

Imprint - When Spellweaver Helix comes into play, you may remove two target sorcery cards in a single graveyard from the game.  (The removed cards are imprinted on this artifact.) ; Whenever a card is played, if it has the same name as one of the imprinted sorcery cards, you may copy the other and play the copy without paying its mana cost.

The imporant thing is the "Whenever a card is played,"  because that means the copy does not trigger it, so you would just get the 2 spells imprinted with trigger spell A once.  

Also, "If you imprint two cards with the same name, it still only makes one copy each time.  [Mirrodin FAQ 2003/10/01]"

Regrowth targets a card in the graveyard, so it needs there to be one on resolution or else it fizzles (is countered).

[Matt]

Note that ALL of a spell's targets must be invalid for it to be countered, not merely any one of them. Important for stuff like Fire/Ice and...Rolling Thunder, I guess.

[Jebus]

Goober nailed it.  Even though you are actually playing the Spell copied from the Helix, the copy isn't a card which is dependent on it triggering.

Thus, it does not create a loop.

Regrowth cannot even be played without a target.  If its target is no longer there upon resolution it is countered.