@is_prefix(s1:string, s2:string)
@is_prefix(s1:string, s2:string, cmp:fct)
@is_prefix(t1:tab, t2:tab)
@is_prefix(t1:tab, t2:tab, cmp:fct)
@is_prefix is an overloaded function. See also @is_suffix and @is_subsequence.

@is_prefix(s1:string, s2:string)
returs true if string s1is a prefix of s2.

@is_prefix(s1:string, s2:string, cmp:fct)
the predicate returns true if s1 is a prefix of s2 where the characters are compared with the function cmp (taking two arguments). The characters are passed to the function cmp as strings of length one.

@is_prefix(t1:tab, t2:tab)
the predicate returns true if t1 is a prefix of t2, that is, if the elements of t1 are the initial elements of t2.

@is_prefix(t1:tab, t2:tab, cmp:fct)
same as the previous version but the function is used to test the equality between the elements, instead of the usual comparison between values. For example: 
       @fun_def cmp($x, $y) { $x > $y }
       @is_prefix([11, 22], [5, 6, 7], @cmp) -> true
true is returned because @cmp(11, 6) and @cmp(22, 7) hold.

See also Predicates @!=    @&&    @||    @<=    @<    @==    @>=    @>    @approx    @arch_darwin    @arch_linux    @arch_windows    @between    @empty    @find    @is_bool    @is_defined    @is_exec    @is_fct    @is_float    @is_function    @is_int    @is_integer_indexed    @is_list    @is_map    @is_nim    @is_numeric    @is_obj    @is_obj_xxx    @is_prefix    @is_string    @is_subsequence    @is_suffix    @is_symbol    @is_undef    @is_vector    @member    @occurs