Let L be the function field of X1(17) over Q. For f in L,  deg(f) is the index [L:Q(f)]. Denote Gal(f) as the Galois group of the normal closure of this extension. L has, up to diamond action, and up to Mobius transformations f -> (a*f+b)/(c*f+d), only three functions of degree 4. We can write L = Q(x,y) where x,y satisfy the equation from Drew's website: Fxy := x^4*y-x^3*y^3-x^3*y+x^2*y^4+x^2*y-x^2-x*y^4+x*y^3-x*y^2+x*y+y^3-2*y^2+y; "The" (unique up to diamond+Mobius) three functions of degree 4 are: x, y, and z := y*(x^2-x*y+y-1)/( (y-1)^2*x ); These functions x,y,z are modular units; their roots and poles are rational cusps. The roots of x-1 and y-1 are rational cusps as well. L = Q(x,y) = Q(x,z) has genus 5 The equation for x,z is: Fxz := x^3*z^4-x^4*z^2-x^3*z^3-x^2*z^4+3*x^3*z^2+2*x^3*z+x*z^3-4*x^2*z-2*x*z^2-x^2+x+z; Q(y,z) is a subfield of index 2 and genus 1 The equation for y,z is: Fyz := y^2*z-y*z^2-y*z+z^2-y; Gal(x) = S4, Gal(y) = D4, and Gal(z) = D4. [note: this does not change if you replace Q by C] So for all but finitely many rational numbers q, the root of x-q resp. y-q resp z-q will give a pair (E,P) defined over a number field K, with P of order 17, and [K:Q] = 4, and Gal(K) is S4 resp. D4 resp. D4 where Gal(K) denotes Gal( normal closure of K ). What are the exceptions? Cuspidal-exceptions: We are not interested in x in {0,1,infinity}, y in {0,1,infinity} or z in {0,infinity} since those give only rational cusps on X1(17). Any non-cuspidal exception will still give (E,P) over K with [K:Q]=4 because there are no non-cuspidal points over fields of degrees 1,2,3. So for D4, a non-cuspidal exception should have Gal(K) = C4 or C2 x C2 since these are the only transitive subgroups. For S4, a non-cuspidal exception should have Gal(K) a subset of D4 or A4 (the maximal subgroups of S4 are D4, A4, or S3 but the last one is not transitive so we can omit it). A rational point on one of the following three curves means that G would be a subgroup of A4 (recall: not interested in cuspidal cases x in {0,1,infinity}, y in {0,1,infinity} or z in {0,infinity}) Px := T^2 - RemoveSquares( discrim(Fxy,y) ); Py := T^2 - RemoveSquares( discrim(Fxy,x) ); Pz := T^2 - RemoveSquares( discrim(Fxz,x) ); Px := T^2-x*(4*x^12-23*x^11+58*x^10-95*x^9+82*x^8-124*x^7+136*x^6-17*x^5-34*x^4-45*x^3+30*x^2+5*x-4); Py := T^2-y^8+4*y^7-8*y^6+10*y^5-10*y^4+8*y^3-y^2-2*y-1; Pz := T^2-z^8+2*z^7-7*z^6+4*z^5-13*z^4-4*z^3-7*z^2-2*z-1; [note: Gal(y) = Gal(z) = D4,  so a non-cuspidal rational point on Py or Pz gives a point on X1(17) defined over a number field with group C2 x C2 since that is the only transitive subgroup of D4 inside A4]. =================== The extension L/Q(x) has degree 4 and group S4. We computed the resolvent polynomial for the subgroup D4 and found this: Pxx := T^3+(-3*x^6+6*x^4-2*x^3-11*x^2+10*x-3)*T^2 +(3*x^12-16*x^11+36*x^10-44*x^9+98*x^8-204*x^7+198*x^6-68*x^5+15*x^4-48*x^3+50*x^2-20*x+3)*T -(x^3-2*x^2+3*x-1)^2*(x^6-6*x^5+6*x^4-x^2-2*x+1)^2 ; which is birational to: Pxx := x*T^3-x*(x-1)^3*T^2+(x-1)*(3*x^2-1)*T+x^2*(x-1); =================== The extension L/Q(y) has degree 4 and group D4.   The polynomial Py tested for C2 x C2 = D4 intersect A4. Remains to test for the subgroup C4.  For this, we need a resolvent polynomial. Denote the 4 roots of Fxy (viewed as univariate polynomial in x over the field Q(y)) as R1,R2,R3,R4 ordered in such a way that Q(y)(R1) = Q(y)(R3). So a potential C4 group would permute them as R1 -> R2 -> R3 -> R4 -> R1 and would thus leave this invariant:         C4inv := R1 * R2^2 + R2 * R3^2 + R3 * R4^2 + R4 * R1^2; That means that C4inv satisfies a degree 2 polynomial in Q(y)[T] and any non-cuspidal rational point on that curve will give us C4. Simplify that polynomial as:  T^2 - RemoveSquares( discriminant ) and we get: Pyy := T^2-(y^8-4*y^7+8*y^6-10*y^5+10*y^4-8*y^3+y^2+2*y+1)*(y-1)*y*(y^2-y-4) ; =================== The extension L/Q(z) has degree 4 and group D4.  Again, compute the minpoly of C4inv, simplify, and we get Pzz := T^2-(z^4-2*z^3+3*z^2+2*z+1)*(z^8-2*z^7+7*z^6-4*z^5+13*z^4+4*z^3+7*z^2+2*z+1); =================== Next, we did a simple search for non-cuspidal points on Px, Py, Pz, Pxx, Pyy, Pzz. The only one we found was y = 1/2 on Pyy giving rise to a non-cuspidal point on X1(17) defined over a number field with group C4. Are there any other examples, or is that it?