BDS
The Problemist, 1984
H#2
(b) wPe2->f3
a) 1.dxe5 Qa6 2.Kd4 Qd3# b) 1.Kd4 Sc4 2.dxc4 Qe4#
The white knight is captured in each solution and the resulting mates are echoes. This was inspired by two of the variations in a directmate problem by Philipp Klett, a selection of whose problems (by John Beasley, published in 1978) I had recently acquired.
Developed and maintained by Brian Stephenson.
Implemented with HTML5, MySQL, Perl (with, inter alia, CGI::Simple, HTML::Template & XML::LibXML) &
CSS/Javascript (jQuery, Bootstrap & DataTables).