PREFIX math: <http://www.w3.org/2000/10/swap/math#>
PREFIX e: <http://eulersharp.sourceforge.net/2003/03swap/log-rules#>
PREFIX polygon: <http://josd.github.io/eye/reasoning/polygon#>

((4 2) (6 2) (7 6) (4 6) (5 5) (5 3) (4 2)) polygon:area 7 .

