I am trying to use R mathematical notation of plotmath in a plot label. In the label, I am trying to use to equality signs, e.g.

ggplot(data=NULL)  
  geom_point(aes(x=0.5, y=0))  
  geom_text(aes(x=0.5, y=-0.1),
            label = paste("x == frac(3,2) == 1.5"), parse=TRUE)  
  xlim(-1,1)  
  ylim(-1, 1)

However, I obtain the following error:

Error in parse(text = text[[i]]) : <text>:1:16: Unexpected '=='
1: x == frac(3,2) ==
                   ^

Is it possible to use two equality signs within a label?

(This is a follow up question to