
	(fiber/new myfun :e123)

blocks error signals and user signals 1, 2 and 3. The signals are as follows: 

	a - block all signals
	d - block debug signals
	e - block error signals
	u - block user signals
	y - block yield signals
	0-9 - block a specific user signal

The sigmask argument also can take environment flags. If any mutually exclusive flags are present, the last flag takes precedence.

	i - inherit the environment from the current fiber
	p - the environment table's prototype is the current environm