st: legends for function graphs

["Richard Hiscock" <rhiscock@netspace.net.au>]

I am trying to create a legend for graphs of functions. Illustrated for 
example by  y=f(x)

twoway function y=(x), xline(0.5, lwidth(thick) lcolor(red) 
lpattern(dash)) xlabel(0(0.1)1)
clwidth(thin) clcolor(blue) clpattern(shortdash_dot)

as an example I wish to add a legend indicating the function - dash line 
= f(x) & the label for the other line - dash_dot = point estimate

I have tried the legend(label 1"") options this seems to need variables 
in data set & does not label functions or xlines/ylines.

Any help would be appreciated
Thanks Richard Hiscock 

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