Note that mod is not in R7RS standard function, so it's not defined in LIPS (it may be in R6RS but no one is using it). In order to run your example you need (define mod modulo) or change mod in the gdc function definition.
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I've created bookmarklet that runs Scheme REPL on any website, you can use it on book or this site. The Scheme implementation is LIPS: my Scheme interpreter written in JavaScript.
Note that
modis not in R7RS standard function, so it's not defined in LIPS (it may be in R6RS but no one is using it). In order to run your example you need(define mod modulo)or changemodin thegdcfunction definition.