Isn't the GPL3 somewhat incompatible with the EPL?
"The EPL and the GPL are not compatible in any combination where the result would be considered either: (a) a "derivative work" (which Eclipse interprets consistent with the definition of that term in the U.S. Copyright Act ) or (b) a work "based on" the GPL code, as that phrase is used in the GPLv2, GPLv3 or the GPL FAQ as applicable. Further, you may not combine EPL and GPL code in any scenario where source code under those licenses are both the same source code module.
Based upon the position of the Free Software Foundation, you may not combine EPL and GPL code in any scenario where linking exists between code made available under those licenses. The above applies to both GPL version 2 and GPL version 3."
The EPL 1.0 is not compatible with the GPL, and a work created by combining a work licensed under the GPL with a work licensed under the EPL cannot be lawfully distributed.
I haven't looked, but Light Table is using some EPL software for sure, starting with ClojureScript itself.