Parsing x * y

[sergey-goncharov]

Here,

// Bouncing ball example
v:=5; p:=10; e:=-0.5;
while true do {
  v'=-9.8, p'=v until_0.01 p<0 /\ v<0;
  v:=e*v; 
}

I am getting a parsing error, which disappears if e*v is replaced with -0.5 * v.