Splitting U(a,b)F
U(a,b)FPrimus splitvaluesSecundus splitvaluesTertius splitvaluesQuartus splitvalues
[1]-Fa+2baa+b-(a-b)
[2]-2a+FbbFb-(a-b)Fb-(a+b)
[3]a-a-bb
[4]Fa-b-Fa+b-aa


Splitting U(a,b)F
the general zero series
Primus
doubled
U(-Fa+2b, Fb-2a)F
doubled
Secundus
doubled
U(a,b)F
doubled
Tertius
doubled
U[a+b, Fb-(a-b)]F
doubled
Quartus
doubled
U[-(a-b), Fb-(a+b)]F
doubled
U-4F4a-F3b-3F2a+2Fb+a=-F*-F3a+F2b+3Fa-2b+a=F2-2*F2a-Fb-a+-a=F2-F-1*F2a+F(a-b)-(a+b)+-b=-F2-F+1*-F2a+F(a+b)+(a-b)+b
U-3F3a-F2b-2Fa+b=-1*-F3a+F2b+3Fa-2b+Fa-b=F*F2a-Fb-a+-Fa+b=F-1*F2a+F(a-b)-(a+b)+-a=-F-1*-F2a+F(a+b)+(a-b)+a
U-2F2a-Fb-a=-1*-F2a+Fb+2a+a=F*Fa-b+-a=F-1*Fa+(a-b)+-b=-F-1*-Fa+(a+b)+b
U-1Fa-b=0*-F2a+Fb+2a+Fa-b=2*Fa-b+-Fa+b=1*Fa+(a-b)+-a=-1*-Fa+(a+b)+a
U0a=0*-Fa+2b+a=2*a+-a=1*a+b+-b=-1*-(a-b)+b
U1b=1*-Fa+2b+Fa-b=F*a+-Fa+b=1*a+b+-a=1*-(a-b)+a
U2Fb-a=1*Fb-2a+a=F*b+-a=1*Fb-(a-b)+-b=1*Fb-(a+b)+b
U3F2b-Fa-b=F*Fb-2a+Fa-b=F2-2*b+-Fa+b=F-1*Fb-(a-b)+-a=F+1*Fb-(a+b)+a
U4F3b-F2a-2Fb+a=F*F2b-Fa-2b+a=F2-2*Fb-a+-a=F-1*F2b-F(a-b)-(a+b)+-b=F+1*F2b-F(a+b)+(a-b)+b
U5F4b-F3a-3F2b+2Fa+b=F2-1*F2b-Fa-2b+Fa-b=F3-3F*Fb-a+-Fa+b=F2-F-1*F2b-F(a-b)-(a+b)+-a=F2+F-1*F2b-F(a+b)+(a-b)+a

Note that the secundus-based split of a zero-series is neutral: what goes in comes out - in this case the general zero-series itself.