[Jprogramming] Dot conjunction in the leap year verb

[ahala2000]

Can anyone show me how's the leap year verb work? I am confused on the use of 
dot. <br/><br/>m11=: 0: ~:/ .= 4 100 400"_ |/ ]   NB. Is y a leap year?<br/>Why 
does it use ~:/ .= here? Is it the same as ~:/@:=   ? <br/><br/><br/><br/>
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