starting Nelson's exercise solutions

.gitignore

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 /.quarto/
 _site
 tikz_*.svg
+.DS_Store

solutions:nelson-niu/finite-sets.jl

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+struct FinSet
+  n::Int
+end
+
+struct FinFunction
+  dom::FinSet
+  codom::FinSet
+  values::Vector{Int}
+end
+
+A, B = FinSet(3), FinSet(2)
+f = FinFunction(A, B, [1,2,2])
+
+function product(X::FinSet, Y::FinSet)
+  x, y = X.n, Y.n
+  P = FinSet(x * y)
+
+  proj_left  = FinFunction(P, X, [i for i in 1:X.n for j in 1:Y.n])
+  proj_right = FinFunction(P, Y, [j for i in 1:X.n for j in 1:Y.n])
+
+  return P, proj_left, proj_right
+end

solutions:nelson-niu/graphs.jl

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+using Catlab, Catlab.CategoricalAlgebra
+
+@present GrphDiagram(FreeSchema) begin
+  E :: Ob
+  V :: Ob
+  src::Hom(E, V)
+  tgt::Hom(E, V)
+end
+
+@acset_type Grph(GrphDiagram, index=[:src,:tgt]) 

solutions:nelson-niu/helloworld.jl

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+println("Hello World")

solutions:nelson-niu/rabbits.jl

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+using Catlab, AlgebraicDynamics, AlgebraicDynamics.UWDDynam
+
+rabbits = ContinuousResourceSharer{Float64}(
+  1,
+  1,
+  (R, p, t) -> p.α*R,
+  [1]
+)

solutions:nelson-niu/uwd-data.jl

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+using Catlab.Programs.RelationalPrograms
+using Catlab.Graphics.GraphvizGraphs
+
+my_uwd = @relation (x, y, z) where (w, x, y, z) begin
+  R(x, w)
+  S(y, w)
+  T(z, w)
+end
+
+to_graphviz(R, box_labels=:name)