diff --git a/engine-proto/engine.jl b/engine-proto/engine.jl
index f2dc981..2f7294a 100644
--- a/engine-proto/engine.jl
+++ b/engine-proto/engine.jl
@@ -87,7 +87,7 @@ struct LiesOn{T} <: Relation{T}
   LiesOn{T}(pt::Point{T}, sph::Sphere{T}) where T = new{T}([pt, sph])
 end
 
-equation(rel::LiesOn) = dot(rel.elements[1].vec, rel.elements[2].vec)
+equation(rel::LiesOn) = mprod(rel.elements[1].vec, rel.elements[2].vec)
 
 # elements: sphere, sphere
 struct AlignsWithBy{T} <: Relation{T}
@@ -97,7 +97,7 @@ struct AlignsWithBy{T} <: Relation{T}
   AlignsWithBy{T}(sph1::Sphere{T}, sph2::Sphere{T}, cos_angle::T) where T = new{T}([sph1, sph2], cos_angle)
 end
 
-equation(rel::AlignsWithBy) = dot(rel.elements[1].vec, rel.elements[2].vec) - rel.cos_angle
+equation(rel::AlignsWithBy) = mprod(rel.elements[1].vec, rel.elements[2].vec) - rel.cos_angle
 
 # --- constructions ---