Question: How do I remove italics from axis labels?

I am writing a textbook in biomedical engineering and using Maple 14 for generating figures.  In many of the graphs, my axis labels have subscripts or superscripts.  For example in a 2D plot statement I type   labels=[x,f[0](x)] which gives a subscript 0.   However, both x and f0(x) appear in italics.  How can I have them appear as normal...i.e. without italics? The labelfont command does not seem to have an instruction to remove the italics.  Can you assist me?

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