eq1 := {
diff(S_h(t),t)= mu_h*(N_h-S_h(t))-(bi_h*b)/(N_h+m)*S_h(t)*I_v(t),
diff(I_h(t),t)=(bi_h*b)/(N_h+m)*S_h(t)*I_v(t)-(mu_h+ga)*I_h(t),
diff(R_h(t),t)=ga*I_h(t)-mu_h*R_h(t),
diff(S_v(t),t)=A-(bi_v*b)/(N_h+m)*S_h(t)*I_h(t)-mu_v*S_v(t),
diff(I_v(t),t)=(bi_v*b)/(N_h+m)*S_v(t)*I_h(t)-mu_h*I_h(t),
mu_h=0.0000457,mu_v=0.25,b=1,ga=0.167,
bi_h=0.4, bi_v=0.4,m=0,N_h=10000,A=5000,
S_h(0)=10000,
I_h(0)=1,R_h(0)=0,S_v(0)=10000,I_v(0)=1
};

f:=x->x^3:
y[1]:=0.5:
y[3]:=subs(x=y[1],f(x)):
i := 2:
y[i] := y[i-1]-(y[1]-y[2+1])*(1/2):
i:=1:
g[i] := (y[i+1]-y[i+2])*x/(y[i]-y[i+1])+(y[i+2]*y[i]-y[i+1]*y[i+1])/(y[i]-y[i+1]):
g[i] := unapply(g[i], x):
h[i] := unapply(solve(y = g[i](x), x), y):
for i from 2 by 1 to 7 do
g[i]:=(f@h[i-1])(x);
g[i]:=unapply(g[i],x);
y[i+2]:=subs(x=y[i+1],g[i](x));
s:=solve(z=g[i](x),x);
h[i]:=unapply(s[1],z);
end do:

for i from -1 by -1 to -8 do

f:=x->x^3:
y[1]:=0.5:
y[3]:=subs(x=0.5,f(x)):
i := 2:
y[i] := y[i-1]-(y[1]-y[2+1])*(1/2):
i:=1:
g[i] := (y[i+1]-y[i+2])*x/(y[i]-y[i+1])+(y[i+2]*y[i]-y[i+1]*y[i+1])/(y[i]-y[i+1]):
g[i] := unapply(g[i], x):
h[i] := unapply(solve(y = g[i](x), x), y):
for i from 2 by 1 to 5 do
g[i]:=(f@h[i-1])(x);
g[i]:=unapply(g[i],x):
s:=solve(y=g[i](x),x):
h[i]:=unapply(s[1],y);
end do;

 for this code i got error "Error, (in kernels)...