  Mathematics can serve many functions in physics. It can provide a
computational system, reflect a physical idea, conveniently encode a rule, and
so forth. A physics student thus has many different options for using
mathematics in his physics problem solving. We present a short example from the
problem solving work of upper level physics students and use it to illustrate
the epistemic framing process: framing because these students are focusing on a
subset of their total math knowledge, epistemic because their choice of subset
relates to what they see (at that particular time) as the nature of the math
knowledge in play. We illustrate how looking for the warrants students use, the
often unspoken reasons they think their evidence supports their mathematical
claims, serves as a window to their epistemic framing. These warrants provide a
powerful, concise piece of evidence of their epistemic framing.
