Define or Extract a Model Formula - Generic Function
DESCRIPTION:
Returns a formula object.

This function is generic (see Methods); method functions can be written to handle specific classes of data. Classes which already have methods for this function include: data.frame, formula, lm, terms.

USAGE: 
formula(object)
as.formula(object)
REQUIRED ARGUMENTS:
object:
either a formula expression (a call to the ~ operator), or an object that defines such an expression, such as a fitted model or a terms object.
VALUE:
an object of class "formula", essentially just the call to ~. The as.formula function differs only in that it will preserve the full class attribute of an object that inherits from class "formula".
SEE ALSO:
formula.object .
EXAMPLES: 
sqrt(skips) ~ . #or, equivalently
formula(sqrt(skips) ~ .)
formula(fuel.fit) # find the formula